Antalya has a Mediterranean climate, so winters are mild compared with most of Northern and Central Europe. You will get plenty of bright, sunny days, but winter is also the rainy season on this coast: expect some grey spells and heavy showers that can last a day or two. Evenings and early mornings feel cool, and the Taurus Mountains behind the city often carry snow on their peaks while the seafront stays green.
The sea is too cool for most people for long swims, so a winter trip is about the city, the countryside and the slower pace rather than the beach. The upside: no crowds at the sights, easy restaurant tables and a chance to see Antalya as residents do.